1. Field of the Invention
The invention relates generally to hinges and more particularly to a door hinge for passing an electrical signal from a wall to a door.
2. Description of the Prior Art
A number of applications exist for a power transfer hinge to pass an electrical current from a wall to a pivotable door or window. Examples of such applications are electrically operated door locks, card-key door locks, door locks that automatically release the door in the event of a fire, door locks that are controllable from a remote location, and door-mounted lights. Several hinge constructions having wires for passing the electrical current have been tried. Preferably the wires are concealed within the hinge to be protected from damage or tampering and the hinge is load bearing to carry the weight of the door. In the known constructions having concealed wires, the wires are routed through longitudinal conduits in plate-like hinge leaves. One figure of merit for a power transfer hinge is the amount of electrical current that can be passed through the wires. However, because it is not desirable for the hinge leaves to be overly thick, the size of the wires in the cable and therefore the current that can be passed through the hinge is limited.
Zychal discloses a hinge for electrically connecting two housings in U.S. Pat. No. 3,428,738 entitled "hinge with conductors passing therethrough". The Zychal hinge comprises a U-shaped hinge plate and an inner hinge plate disposed longitudinally within the U. A wire cable is routed from recesses in each leg of the U-shaped plate to a recess in the inner plate through a longitudinal channel along an axis about which pivoting occurs. The housings are structurally connected for pivoting by two separate load-bearing hinges. Zychal does not teach the details of a load bearing hinge and the Zychal hinge is not intended or suitable for supporting a door.
Crane et al. in U.S. Pat. No. 3,857,625, Suska in U.S. Pat. No. 4,412,711, and O'Brien, II in U.S. Pat. No. 4,839,939 disclose hinges having wires entering an opening in the rear of a first hinge leaf, passing through a longitudinal conduit in the first leaf, passing upwardly or downwardly through bores in knuckles of the first and a second hinge leaf along the pivot axis of the hinge, passing through a second longitudinal conduit in the second hinge leaf, and exiting out an opening in the second hinge leaf. Unlike, Zychal, each of these hinges is intended to be load bearing, however, the constructions require several specialized parts and machining operations and are relatively complex and costly compared to a standard door hinge. Further, the hinges must be partially or entirely disassembled to insert or remove the wires, thereby making the hinge more difficult to repair if a wire breaks.
Several commercial products are available that comprise a standard door hinge that has been modified to pass a wire cable upwardly or downwardly through the bores of the hinge knuckles and outwardly through longitudinal passageways in the hinge leaves. The wire cable then exits to the door jam and wall jamb through recesses in the rear of the hinge leaves. The longitudinal passageways are gun drilled from the outside edge of the hinge leaves through the recesses to the bores of the hinge knuckles. Two conducting wires are required in order to make a complete electrical circuit for an electrical application device in the door. However, four wires are typically used to more closely approximate a circular cross-section of the longitudinal passageways to increase the amount of electrical current that can be carried and to facilitate the routing of the wire cable. For a commercial application, these products have the potential benefits being easy to install because they fit a standard door and wall jamb and of low cost due to the high manufacturing volume of the standard door hinges. However, all known commercial products require expensive machining operations for modifying the standard hinges and must be disassembled to replace the wire cable if the wires break.
There is a need for a load-bearing power transfer hinge that uses a concealed electrical cable for passing electricity from a wall to a door that carries the maximum electrical current, is relatively simple and inexpensive to construct, and can be repaired without disassembly.